Method of influencing the chemical and physical properties of blast furnace slags



Get. 20, 1936 J. ROLL ETHOD OF FLUENCING THE CHEM L AND PHYSIC SLAGS PRRTIES OF BLAS UR E Filed Oct. 1935 JOSEF FoLL,

ATTORNEY Patented a.. 20, 1936 PATENT OFFICE METHOD OF INFLUENCING THECHEMICAL AND PHYSICAL PROPERTIES OF BLAST FURNACE SLAGS Josef Roll,Hamborn-Bruckhausen, Germany I Application October 15, 1935, Serial No.45,145 Claims. (01. 75-41) The slag which is accumulated when workingthe blast furnace has gained more and more in importance during recentyears and now represents an important lay-product of every blastfurnace. The slags can be used among other purposes for the manufactureof road making materials, such as road metal and foundation material,and for ballast and the like and railroad tracks and also in themanufacture of tarmacadam. The slag can also be used in the man-,ufacture of paving stones and the like. Owing to the high requirementswhich modern street and railway traffic imposes on the materials, onlyblast furnace slags of a uniform and basaltic character can be used forthe purposes mentioned.

Now dense and homogeneous blast furnace slags of this kind have adefinite chemical composition and must contain an excess of silicicacid. For metallurgical reasons, however, slags with a suitably highcontent of $102 are not usually melted in the blast furnace. The slagsfrequently have a pronounced basic character, that is they have a highcontent of CaO for binding the sulphur. Basic slags, however, areinclined to crumble and they therefore cannot be employed for theproduction of a dense, basalt-like and resist- Y ant material which issuitable for road making for example.

Experiments have previously been made with a view to improving theseuseless basic slags. Thus, attempts have been made to make these slagsacid and useful by the addition of substances containing silicic acid oralumina after the slag was tapped from the blast furnace. Theseexperiments, however, did not lead to any satisfactory result becausethe slag cooled down too rapidly and the substances which were addedoutside the blast furnace after the slag had,been tapped could o nolonger be brought completely into solution.

Likewise processes in which the slag was de-sulphurized and made thinlyliquid by blowing compressed air through it have, up to the present, notproved successful because the slag solidified too rapidly with suchtreatment.

By the process of the present invention, the chemical and physicalproperties of blast furnace slags are influenced in the following mannerand the slags are made useful for the purposes indicated.

For carrying out the metallurgical process in the blast furnace, arelatively basic slag, the character of which depends upon the qualityof the pig iron which it is desired to produce, is

melted. In the manufacture of Thomas pig-iron for example such a slagnormally has approximately the following composition:31-32% SlOz,

42-43% CaO, 11-12% A1203, 5-6% MgO. Now a slag of this composition,owing to the unfavorable ratio of SlOziCaO contained in it is inclinedto crumble and does not have a sufiiciently basaltlike character for useas road-making material. Therefore, according to the present invention,a definite quantity of silic acid (silica), for example in the form offine dried sand, is blown into the 10 hearth-casing of the blast furnaceduring the blast period. The sand is introduced into the hearth-casingof the blast furnace below the main twyers, for example, by means of anapparatus similar to a sand blasting apparatus. For con- 15 veying thesand, compressed air or gases, for ex,- ample blast furnace gas, can beemployed. It has been found by experience that, on the one hand, thetemperatures prevailing in the hearth are suflicient to bring thematerial which is blownin into solution and that, on the other hand, noreaction by which the quality of the pig-iron is impaired takes placebetween the slag and the molten pig-iron.

The slags which are obtained in the manner 25 described have, aftersolidification, a dense and quite homogeneous structure and, owing totheir uniform basalt-like character, are able to satisfy all therequirements demanded from them. At the same time, the new process ofimproving the slag can be carried out easily and at a relatively smallexpense.

The accompanying drawing illustrates, by way of example, a blast furnaceprovided with an apparatus which can be used for carrying out theprocess according to the invention.

Referring to the drawing, a nozzle 2 is introduced into the furnacethrough the casing l of the hearth. The mouth 3 of the nozzle issituated below the plane I--I which passes through the twyers 4. Theslag is tapped 011 through the tap hole 5. The sand which is blown intothe blast furnace is conducted to the nozzle 2 through a pipe 6 which isconnected at 1 to an air or gas compressor. The sand falls into the pipe6 45 from a container 8, the upper part of which is in connectionthrough the pipe 9 with the conduit for the compressed air or gas.

The described apparatus for supplying the sand has proved to be verysuitable but it will be un- 50 derstood that other methods of supplyingthe material to be blown in can also be employed.

I claim:

1. The method of influencing the chemical and physical properties ofblast furnace slags which 55 4. The method of influencing the chemicaland physical properties of blast furnace slags which consists inblowingsand by means of blast furnace gasunder pressure into thehearth-casing of the blast furnace below the plane passing through thetwyers.

5. The method of influencing the chemical and physical properties ofblast furnace slags which consists in blowing sand by means ofcompressed air into the hearth casing of the blast furnace 10 below theplane passing through the twyers.

J OSEF ROLL.

